This invention relates to electrically commutated motors, and more particularly, to methods and approaches used to control the operating characteristics of an electrically commutated motor, specifically, emulating operation of an induction motor.
Electrically commutated motors (ECMs) are used in a wide variety of systems operating in a wide variety of industries. As such, the ECMs are subject to many operating conditions and often, the operating conditions necessitate that the operating characteristics of the ECM be changed to match the requirements of the associated application (i.e. different speeds or airflow requirements for heating, cooling, and constant fan for residential HVAC applications). Because of the complexity of the many possible desired operating characteristics, it may be difficult to remove, for example, an induction motor from one system and replace it with an ECM. More specifically, the ECM control circuits and interfaces must typically be changed to enable the ECM to operate with different operating characteristics in different applications.
In a furnace or air conditioning blower system, the speed torque characteristics become an integral part of the design and ratings of that system. When such a system is upgraded to use a brushless DC motor (ECM), rather than an induction motor, the characteristics that depend on the speed torque curve of the induction motor have to be re-evaluated. The re-evaluation occurs since the ECM motor does not have the same characteristic speed torque curve, and in fact is quite likely to have a performance envelope that includes a capability of operating at several hundred RPM faster than the induction motor's capabilities. This operational characteristic of an ECM can result in the target blower system having higher wheel speeds under some conditions than it did when the blower system was equipped with an induction motor. Another result of replacing the induction motor with the ECM is that fault condition operation or safety limit functions, for example, over temperature limit switch operation, is different within an ECM. As such, these operations and function are typically retested and validated upon replacement of an induction motor with an ECM. Retesting and validation of motor operation is expensive.